Imaging apparatus with strobe consecutive shooting mode

ABSTRACT

When the mode is set to a strobe consecutive shooting mode, an imaging apparatus sets the mode to a pixel addition drive mode for reading out image data using pixel addition drive (S 7 ), performs metering operation using preliminary flashing (S 8 ) and calculates an appropriate amount of flashing on the basis of the metering operation (S 9 ). Next, the imaging apparatus judges whether or not it is possible to flash three times consecutively with the calculated amount of flashing (S 10 ). If it is judged that it is not possible to flash three times consecutively with the calculated amount of flashing (NO in S 10 ), the imaging apparatus limits the amount of flashing to the largest amount of flashing within the range of amounts of flashing with which flashing of strobe light three times consecutively is possible (S 11 ), and performs strobe consecutive shooting with the limited amount of flashing (S 13  to S 17 ).

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2005-355964 filed on Dec. 9,2005, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an imaging apparatus and an imagingmethod, and specifically to an imaging apparatus and an imaging methodfor shooting an object by flashing strobe light.

2. Description of the Related Art

In an imaging apparatus, for example, a digital camera, of recent years,strobe light needs be flashed for each shooting in the case where anobject is to be shot consecutively in a dark condition.

However, if strobe light is consecutively flashed, the voltageaccumulated in a capacitor decreases. Accordingly, exposure sufficientfor shooting cannot be obtained.

Therefore, an art has appeared for performing strobe shooting for aflash time corresponding to a time code and a number of consecutiveshootings and compensating insufficiency in the amount of exposure byincreasing the gain.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, there is providedan imaging apparatus comprising: an image pickup element for convertinglight of an object to image data; a strobe for flashing and firinglight; a shooting unit which performs strobe shooting using the imagepickup element and the strobe; a calculation unit which calculates anamount of flashing of the strobe with which appropriate exposure isobtained during the strobe shooting performed by the shooting unit; ajudgment unit which judges whether or not it is possible for the strobeto flash consecutively for a certain number of times with the amount offlashing calculated by the calculation unit; and a shooting control unitwhich has the shooting unit execute consecutive strobe shooting for thecertain number of times with the amount of flashing with whichconsecutive flashing for the certain number of times is possible, andhas the shooting unit drive the image pickup element by pixel addition,in the case where it is judged by the judgment unit that consecutiveflashing by the strobe for the certain number of times with the amountof flashing calculated by the calculation unit is not possible.

In accordance with another aspect of the present invention, there isprovided an imaging apparatus comprising: an image pickup element forconverting light of an object to image data; a strobe for flashing andfiring light; a shooting unit which performs strobe shooting using theimage pickup element and the strobe; a setting unit which sets a strobeconsecutive shooting mode in which strobe shooting is consecutivelyexecuted by the shooting unit; and a shooting control unit which has theshooting unit drive the image pickup element by pixel addition, in thecase where the strobe consecutive shooting mode is set by the settingunit.

In accordance with another aspect of the present invention, there isprovided an imaging method comprising: a shooting step of performingstrobe shooting using an image pickup element for converting light of anobject to image data and a strobe for flashing and firing light; acalculation step of calculating an amount of flashing of the strobe withwhich appropriate exposure is obtained during the strobe shootingperformed by the shooting step; and a judgment step of judging whetheror not it is possible for the strobe to flash consecutively for acertain number of times with the amount of flashing calculated by thecalculation step; wherein, the shooting step executes consecutive strobeshooting for the certain number of times with the amount of flashingwith which consecutive flashing for the certain number of times ispossible, and drives the image pickup element by pixel addition, in thecase where it is judged by the judgment step that consecutive flashingby the strobe for the certain number of times with the amount offlashing calculated by the calculation step is not possible.

According to the present invention, since imaging elements are driven bypixel addition, it is possible to prevent the image quality from beingdeteriorated during strobe consecutive shooting.

The above and further objects and novel features of the presentinvention will more fully appear from the following detailed descriptionwhen the same is read in conjunction with the accompanying drawings. Itis to be expressly understood, however, that the drawings are for thepurpose of illustration only and are not intended as a definition of thelimits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a digital camera in an embodiment of thepresent invention;

FIG. 2 is a flowchart showing an operation of the digital cameraaccording to the embodiment;

FIG. 3 is a flowchart showing an operation of the digital cameraaccording to a modification;

FIG. 4 is a time chart showing a voltage of a built-in capacitor C, astrobe flash pulse, and an operation of the camera in a strobeconsecutive shooting mode;

FIG. 5A is a diagram showing the state of a correction coefficienttable;

FIG. 5B is a diagram showing the state of the correction coefficienttable;

FIG. 6A is a diagram for describing judgment on whether or not the imagedata has adequate brightness and brightness correction using gammacorrection;

FIG. 6B is a diagram for describing gamma correction processing; and

FIG. 7 is a flowchart showing an operation of a digital camera in amodification of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the preferred embodiments of the present invention will bedescribed with reference to the drawings as an example of application ofan imaging apparatus of the present invention to a digital camera.

A. First Embodiment

A-1. Configuration of the Digital Camera

FIG. 1 is a block diagram showing the general electrical outlineconfiguration of a digital cameral 1 which actualizes the imagingapparatus of the present invention.

The digital camera 1 includes a focus lens 2, a zoom lens 3, a lensdriver circuit 4, a CCD 5, a vertical driver 6, a timing generator (TG)7, a pre-processing unit 8, a memory 9, a CPU 10, a DRAM 11, an imagedisplay section 12, a flash memory 13, a key input section 14, a strobeunit 15, and a bus 16.

The focus lens 2 and the zoom lens 3 are configured with a plurality oflens groups, and the lens driver circuit 4 is connected to the focuslens 2 and the zoom lens 3.

The lens driver circuit 4 is configured by motors (not shown) for movingthe focus lens 2 and the zoom lens 3 in the axial directions thereof,respectively, and motor drivers (not shown) for driving the focus motorand the zoom motor, respectively, according to a control signal which issent from the CPU 10.

The CCD 5, scan-driven by the vertical driver 6, photo-electricallyconverts the intensity of light of the respective colors in the RGBvalue of an object image at a constant cycle period, and outputs theintensity to the pre-processing unit 8 as imaging samples. The operationtiming of the vertical driver 6 and the pre-processing unit 8 iscontrolled by the CPU 10 via the TG 7.

The TG 7 is connected with the pre-processing unit 8 which is configuredwith a correlated double sampling (CDS) circuit for performingcorrelated double sampling of imaging signals (image data) that isoutputted from the CCD 5 and holding them, an automatic gain control(AGC) circuit for performing automatic gain control of the sampledimaging signals, and an analog to digital (A/D) converter for convertingthe automatic-gain-controlled analog imaging signals to digital signals.The imaging signals from the CCD 5 are sent as digital signals to theCPU 10 via the pre-processing unit 8.

The CPU 10 is a one-chip microcomputer which has functions of performingimage processing including gamma (γ) correction processing, pixelinterpolation processing, white balance processing, histogram generationprocessing, and generation processing of luminosity color differencesignals (YUV signals) and the like and compression and expansionprocessing (for example, and compression and expansion in a jointphotographic experts group (JPEG) format) to individual image data sentfrom the pre-processing unit 8, and which controls the individualsections of the digital camera 1.

Particularly in the present embodiment, the CPU 10 has functions ofcontrolling start of flashing and flash time of the strobe unit 15,calculating an amount of flashing on the basis of a metering operationand the result thereof, and performing strobe consecutive shooting andbrightness correction processing.

The memory 9 accommodates a control program necessary for controllingindividual sections of the CPU 10 and necessary data, and the CPU 10operates in accordance with the program.

In addition, the memory 9 records a correction coefficient table inwhich correction coefficients of flash time for individual number ofimages that are consecutively shot in the strobe consecutive shooting.The correction coefficient table will be described later. In addition,the memory 9 has a flash time storage area for storing the flash time ofthe strobe and a shooting number storage area for storing the number ofshootings.

The DRAM 11 is used as a buffer memory for temporarily storing imagedata that is sent to the CPU 10 after imaged by the CCD 5, and is alsoused as a working memory for the CPU 10.

The image display section 12 includes a color liquid crystal display(LCD) and a driver circuit therefor. It displays the object imaged bythe CCD 5 as a through image in the stand-by mode, and displays theimage data which has been read out from the flash memory 13 and expandedwhile reproducing a recorded image.

The flash memory 13 is a storage medium for storing the image data orthe like which has been picked up by the CCD 5.

The key input section 14 includes a plurality of operation keys, such asa shutter button and a mode selection key, and outputs operation signalscorresponding to a key operation by a user to the CPU 10.

The strobe unit 15 includes a built-in capacitor C, a charging circuit(not shown), a flash circuit (not shown) including a xenon tube, acharged voltage detection circuit (not shown) of the capacitor C, notshown, and the like. The charging circuit charges an electric power tothe built-in capacitor C, and the flash circuit supplies an electriccharge in the built-in capacitor C to the xenon tube which serves as alight source, thereby flashing and firing light. The strobe unit 15 iscontrolled by the CPU 10 for the start of charging, flashing and flashtime, and the strobe unit 15 performs flashing or the like according tothe control. In addition, the charged voltage detection circuit in thestrobe unit 15 sends a charged voltage it has detected to the CPU 10.

A-2. Operation of the Digital Camera 1

Next, the operation of the digital camera 1 in the embodiment will beexplained according to the flowcharts in FIGS. 2 and 3 and the timechart in FIG. 4. FIG. 4 is a time chart showing the voltage of thebuilt-in capacitor C, a strobe flash pulse, and the operation of thecamera in the strobe consecutive shooting mode.

When the mode is set to the strobe shooting mode by operation by a userof the mode selection key of the key input section 14, the CPU 10 startsa through image display in which the CCD 5 starts imaging an object,generates luminosity color difference signals from the image dataacquired by the imaging, stores the generated image data in theluminosity color difference signals to the buffer memory (DRAM 11), anddisplays the stored image data of the object to the image displaysection 12 (Step S1).

Subsequently, the CPU 10 judges whether or not the strobe consecutiveshooting mode has been selected by the user (Step S2). The judgment ismade based on whether or not an operational signal corresponding to theoperation of selecting the strobe consecutive shooting mode has beensent from the key input section 14. The strobe consecutive shooting modeherein refers to a mode. for shooting an object consecutively (threetimes consecutively in this case) and flashing strobe light for eachshooting.

If the CPU 10 judges in Step S2 that the strobe consecutive shootingmode has not been selected, the CPU 10 judges whether or not a strobesingle shooting mode has been selected (Step S3). The judgment is madebased on whether or not an operational signal corresponding to theoperation of selecting the strobe single shooting mode has been sentfrom the key input section 14. The strobe single shooting mode hereinrefers to a mode for flashing strobe light and shooting an object once.

If the CPU 10 judges in Step S3 that the strobe single shooting mode hasnot been selected, the CPU 10 returns to Step S2.

On the other hand, if the CPU 10 judges in Step S2 that the mode hasbeen set to the strobe consecutive shooting mode, the CPU 10 sends acontrol signal to the strobe unit 15, thereby starting a charging of thebuilt-in capacitor C (Step S4). At this time, the charging circuit ofthe strobe unit 15 charges the built-in capacitor C in accordance withthe control signal from the CPU 10.

After starting charging, the CPU 10 judges whether or not the chargingis complete (Step S5). The judgment on whether or not the charging iscomplete is made based on charged voltage information sent from thecharged voltage detection circuit of the strobe unit 15.

If the CPU 10 judges in Step S5 that the charging is not complete, theCPU 10 remains at Step S5 until the charging is complete. On the otherhand, if the CPU 10 judges that the charging is complete, the CPU 10judges whether or not the shutter button has been depressed (Step S6).The judgment is made based on whether or not an operational signalcorresponding to the depression of the shutter button has been sent fromthe key input section 14.

It is apparent from FIG. 4 that the voltage of the built-in capacitor Cincreases upon the start of the charging, the charging is complete whenthe voltage of the built-in capacitor C has reached a certain voltage(which is assumed to be 300 V in this case), and the voltage does notincrease further.

If the CPU 10 judges in Step S6 that the shutter button has beendepressed, the CPU 10 sets the mode to a pixel addition drive mode (StepS7). At this time, the CPU 10 also sets the number of pixels to beadded. The pixel addition drive mode refers to a mode for reading out anelectric charge accumulated in the CCD 5 using pixel addition drive. Forexample, pieces of pixel information for a plurality of lines are addedfor each row, and a signal acquired by the addition is outputted fromthe CCD 5 as a signal corresponding to one pixel.

The reason for setting the mode to the pixel addition drive mode is asfollows. When a consecutive shooting (continuous shooting) is performed,the voltage of the built-in capacitor C is split into three for flashingstrobe light, which may lead to an insufficient amount of flashing. Thisinsufficient amount of flashing can be compensated by reading out theelectric charge accumulated in the CCD 5 using the pixel addition drivemode. At the same time, the frame rate can be enhanced by increasing anelectric charge read-out rate of the CCD 5, thereby enabling fasterconsecutive shooting.

Subsequently, the CPU 10 performs a metering operation using preliminaryflashing (Step S8). That is, the CPU 10 performs processing ofpreliminary flashing strobe light by sending a control signal to thestrobe unit 15, and at the same time having the CCD 5 perform a shooting(electric charge accumulation) operation and subsequently reading outthe electric charges accumulated in the CCD 5 using the pixel additiondrive. Because of preliminary flashing in this case, the flash time isshorter than that during the strobe shooting, and it is assumed to be 10μsec in this case.

It is apparent from FIG. 4 that during the metering operation the CPU 10sends the control signals on the start of flashing and flash time (i.e.,strobe flash pulse) to the strobe unit 15, the flash circuit in thestrobe unit 15 fires light by discharging electric charges in thebuilt-in capacitor C, and therefore, the voltage in the built-incapacitor C has dropped from 300 V to 295 V.

Subsequently, the CPU 10 calculates the amount of flashing of the strobelight to be flashed on the basis of the result of the metering operation(Step S9).

The calculation of the amount of flashing is made on the basis of theaverage value of the luminosity of the image data (or a part of theimage data) which has been read out by the pixel addition drive and ismade so as to calculate the amount of flashing of strobe light to beflashed with which an appropriate exposure is acquired. Furthermore, inthis case, a strobe flash time of the first picture (or the firstshooting) which provides the calculated amount of flashing is calculatedand stored in the flash time storage area in the memory 9.

Subsequently, the CPU 10 judges whether or not the strobe consecutiveshooting is possible with the calculated amount of flashing (Step S10).That is, since shootings are performed three times consecutively in thestrobe consecutive shooting, the CPU 10 judges whether or not thevoltage corresponding to the amount for flashing strobe light threetimes consecutively is accumulated in the built-in capacitor C.

In this case, it is judged whether or not the first strobe flash timecalculated in Step S9 is equal to or smaller than a limit value (whichis assumed to be 24 μsec in this case). If the first strobe flash timeis judged to be equal to or smaller than 24 μsec, it is judged that thevoltage corresponding to the amount for flashing strobe light threetimes consecutively with the calculated amount of flashing isaccumulated in the built-in capacitor C.

The reason why the judgment on whether or not it is possible to flashthree times consecutively with the calculated amount of flashing is madebased on whether or not the first flash time is equal to or smaller than24 μsec will be specifically described as below.

Supposing that shooting is performed three times consecutively with auniform amount of flashing, the voltage in the capacitor C drops aftereach flashing. Therefore, to achieve three consecutive flashings with auniform amount of flashing, the flash time need be longer as the numberof flashings increases. The flash time of the strobe light for eachshooting can be determined by the correction efficient tableaccommodated in the memory 9, and the flash time t of strobe light foreach shooting is determined by the equation, t=correction coefficient Xthe first flash time.

FIGS. 5A and 5B show the states of the correction coefficient tablesaccommodated in the memory 9.

It is understood from FIG. 5A that since the correction coefficient forthe first flash time is 1.00, the first flash time shall be 1.00 X thefirst flash time. Since the correction coefficient for the second flashtime is 1.18, the second flash time shall be 1.18 X the first flashtime. Further, since the correction coefficient for the third flash timeis 1.36, the third flash time shall be 1.36 X the first flash time.

It goes without saying that the correction coefficients are provided insuch a manner that the amounts of flashing do not vary for individualshootings, although the flash times for each shooting are varied by thecorrection coefficients.

In addition, with reference to FIG. 4, the minimum flash enablingvoltage is 260 V, which refers to the minimum voltage required forperforming the third flashing.

According to the circumstance as described above, if the first flashtime is obtained, the second flash time will also be determined, wherebythe voltage of the built-in capacitor C will also be determined when thesecond flash ends.

For example, in the case where the first strobe flash time is 28 μ sec,the second strobe flash time will be approximately 33 μ sec, and thevoltage of the built-in capacitor C during the third strobe flashing(when the second strobe flashing ends) will be 256 V. Accordingly, it isnot possible to perform the third strobe flashing. On the other hand, inthe case where the first strobe flash time is 24 μ sec, the secondstrobe flash time will be approximately 28 μ sec, and the voltage of thebuilt-in capacitor during the third strobe flash will be 267 V.Accordingly, it is possible to perform the third strobe flashing.

In this case, therefore, judgment on whether or not it is possible toflash strobe light three times consecutively with a uniform amount offlashing is made based on whether or not the first strobe flash time isequal to or smaller than 24 μsec. Note that in FIG. 4, an example isshown of a case in which recharging of the built-in capacitor C is beingstopped after the built-in capacitor is charged and at least until aseries of consecutive strobe shootings end.

If the CPU 10 judges in Step S10 that the strobe consecutive shooting isnot possible with the calculated amount of flashing, that is, if itjudges that the first flash time is not equal to 24 μsec or less, theCPU 10 limits the amount of flashing of strobe light for the firstpicture to 24 μsec (Step S11) and proceeds to Step S12. That is, if theCPU 10 judges that the first flash time is not 24 μ sec or less, itupdates what is stored in the flash time storage area in the memory 9 to24 μsec.

On the other hand, if the CPU 10 judges that the strobe. consecutiveshooting is possible with the calculated amount of flashing, that is, ifit judges that the first flash time is equal to or smaller than 24 μsec,the CPU 10 proceeds to Step S12 as it is.

When the CPU 10 proceeds to Step S12, the CPU 10 determines the amountof flashing on the basis of the flash time stored in the memory 9 as theabsolute amount of flashing.

In other words, in the case where the flash time (which is proportionalto the amount of flashing) calculated in Step S9 is 24 μsec or less, theCPU 10 determines the calculated flash time as the absolute amount offlashing. On the other hand, in the case where the flash time calculatedin Step S9 is longer than 24 μsec, the CPU 10 determines 24 μsec as theabsolute amount of flashing.

At this time, the CPU 10 sets the number of shootings n to 1, that is,stores 1 in the shooting number storage area in the memory 9. In thiscase, it is assumed that the flash time which has been determined is 24μsec.

Subsequently, the CPU 10 performs correction of the strobe flash time(Step S13). The correction is performed by reading out the correctioncoefficient corresponding to the number of shootings (the number oftimes) stored in the shooting number storage area in the memory 9 andmultiplying the read-out correction coefficient and the determined flashtime (i.e., the. flash time stored in the flash time storage area).

In this case, since the determined flash time is 24 μsec and the storednumber of shootings is 1, the correction coefficient corresponding tothe first picture shall be 1.00. Accordingly on the basis of 24 μsec X1.00, the flash time after the correction shall be 24 μsec.

Subsequently, the CPU 10 sets the flash time after the correction as thestrobe flash time (Step S14), and performs a strobe shooting operation(an operation of exposing the CCD 5 and an operation of flashing thestrobe unit 15) on the basis of the set strobe flash time (Step S15).Note that in the strobe shooting operation, electric charges accumulatedin the CCD 5 are read out by the pixel addition drive, and still-imagedata acquired by the strobe shooting is stored in the buffer memory.

Subsequently, the CPU 10 judges whether or not strobe shooting has beenperformed three times (Step S16). If the CPU 10 judges S16 that strobeshooting has not been performed three times, the CPU 10 increments thenumber of shootings n (Step S17) and returns to Step S13. On the otherhand, if the CPU 10 judges in Step S16 that strobe shooting has beenperformed three times, the CPU 10 proceeds to Step S24.

The judgment on whether or not strobe shooting has been performed threetimes is made based on whether or not the number stored in the shootingnumber storage area has reached 3. In addition, the number of shootingsn is incremented by storing the number which is determined by adding +1to the number stored in the shooting number storage area.

On the other hand, if the CPU 10 judges in Step S3 that the mode is setto the strobe single shooting mode, the CPU 10 sends a control signal tothe strobe unit 15, thereby starting charging of the built-in capacitorC (Step S18).

After starting charging, the CPU 10 judges whether or not charging iscomplete (Step S19).

If the CPU 10 judges in Step S19 that charging is not complete, the CPU10 remains at Step S19 until charging is complete. If the CPU 10 judgesthat charging is complete, the CPU 10 judges whether or not the shutterbutton has been depressed (Step S20).

If the CPU 10 judges in Step S20 that the shutter button has not beendepressed, the CPU 10 remains at Step S20 until the shutter button isdepressed. When the shutter button is depressed, the CPU 10 performs ametering operation using preliminary flashing (Step S21). During themetering operation, pixel addition drive is not performed. Instead,pixels in the CCD 5 are read out by an ordinary read-out drive (such asall-pixels read-out drive and part of pixels read-out drive).

Subsequently, the CPU 10 sets the amount of flashing with whichappropriate exposure is achieved on the basis of the result of themetering operation (Step S22), performs a strobe shooting operation onthe basis of the set amount of flashing (Step S23), and proceeds to StepS24. Note that in the strobe shooting operation, electric chargesaccumulated in the CCD 5 are read out by an ordinary read out drive, andstill image data acquired by the strobe shooting is stored in the buffermemory.

Note that if the case where the metering operation is performed in thestrobe consecutive shooting mode is compared with the case where themetering operation is performed in the strobe single shooting mode underthe same shooting conditions, the amount of flashing calculated in StepS9 in FIG. 2 on the basis of the result of the metering operation issmaller than the amount of flashing set in Step S22 on the basis of theresult of the metering operation. This is because the image data in theCCD 5 is read out by pixel addition drive in the strobe consecutiveshooting mode, whereby luminosity of the whole image has increased.

When the CPU 10 proceeds to Step S24, the CPU 10 judges whether or notthe still image data (Bayer data) acquired by the strobe shooting hasadequate brightness. In the case where a plurality of still image datais acquired by the strobe consecutive shooting, the CPU 10 judgeswhether or not the individual still image data that has been acquiredhas adequate brightness.

The CPU 10 performs brightness correction using gamma correction to thestill image data in the Bayer data format which has been judged in StepS24 not to have adequate brightness (Step S25), and records the stillimage data in the flash memory 13. At this time, when recording stillimage data, the CPU 10 performs image processing such as processing ofgenerating luminosity color difference signals, compresses the processedimage data and records the compressed data.

On the other hand, the CPU 10 records the still image data in the Bayerdata format which has been judged to have adequate brightness in StepS24 in the flash memory 13 as they are. Also in this case, whenrecording still image data, the CPU 10 performs image processing such asprocessing of generating luminosity color difference signals, compressesthe processed image data and records the compressed data.

An example of the judgment on whether or not the still image data hasadequate brightness, and of the method of correcting brightness usinggamma correction will be briefly described hereafter.

The judgment on whether or not the still image data has adequatebrightness is made by generating a histogram for each RGB from the Bayerdata, which is the still image data acquired by the shooting, anddetecting a level at which a high luminosity ratio is achieved for eachRGB (for example, the level at which 3% from the high luminosity end isachieved). Next, judgment is made by selecting the highest value amongthe levels at which the high luminosity ratios are achieved for each RGB(hereinafter referred to as peak levels). If the selected value ishigher than a threshold, it is judged that the still image data hasadequate brightness.

FIG. 6A shows a histogram generated for each RGB with the left sidebeing “black” and the right side being “white”. Each histogram isrepresented by 10-bit digital values (1024 values).

A shaded portion in the histogram for each RGB shows a portion until 3%is achieved starting from the high luminosity end, and the portion atwhich the exact 3% is achieved is considered as the peak level. The peaklevels for individual RGBs shall be set as R-PEAK, G-PEAK and B-PEAK,respectively.

For example, when it is assumed that R-PEAK=547, G-PEAK=541 andB-PEAK=543 in FIG. 6A, the highest value will be R-PEAK=547.

In FIG. 6A, since the highest value R-PEAK=547 is not higher than thethreshold, it is judged that the still image data does not havebrightness.

Subsequently, the method for correcting brightness using gammacorrection calculates a correction ratio which makes the selectedhighest value the threshold. As shown in FIG. 6B, the gamma curve of 1.0time has been determined in advance as the standard. With respect tothis standard, the curve is changed in a manner to reduce the inputrange, corresponding to the correction ratio such as 1.5 times or 2.0times. Accordingly, for example, from a gamma curve whose correctionratio has been changed to 1.5 times, an output value b2 is obtained foran input value a1. That means that a value of higher brightness can beobtained than an output value b1 obtained from the standard curve.

A-3. Effects

As described above, in the present embodiment, judgment is made onwhether or not strobe flashing is possible three times consecutivelywith the amount of flashing calculated on the basis of the result of themetering operation. In the case where it is judged that consecutivestrobe flashing is possible, strobe consecutive shooting is performedwith the calculated amount of flashing. Accordingly, image data freefrom insufficient exposure can be acquired without image quality beingdeteriorated.

On the other hand, in the case where consecutive strobe flashing is notpossible, the amount of flashing of the strobe is limited to the largestpossible value within the range of the amounts with which consecutivestrobe shooting is possible, and strobe consecutive shooting isperformed with the limited amount of flashing. Accordingly, it ispossible to prevent insufficient exposure as much as possible withoutthe image quality being deteriorated.

In addition, in the case where the mode is set to the strobe consecutiveshooting mode, the metering operation is performed after the driving ofthe CCD 5 is set to the pixel addition drive, and the amount of flashingis calculated on the basis of the result of the metering operation.Accordingly, the luminosity of the whole image data which has been readout from the CCD 5 increases, thereby decreasing the calculated amountof flashing. In addition, since it is possible to decrease thecalculated amount of flashing, the judgment that strobe consecutiveshooting is not possible with the calculated amount of flashing is madeless frequently, whereby it is more likely that the image data free frominsufficient amount of light is achieved.

In addition, since the strobe shooting is performed by pixel additiondrive, luminosity of the whole image data acquired by shootingincreases, whereby it is more likely that the image data free frominsufficient amount of light is achieved.

In addition, it is judged whether or not individual image data hasadequate brightness, and then brightness correction using gammacorrection is made on image data which does not have adequatebrightness. Accordingly, it is possible to acquire image data free frominsufficient exposure. In addition, even in the case where brightnesscorrection is to be performed to image data, acquiring the image datawith the largest possible amount of flashing within the range of amountswith which strobe consecutive shooting is possible. Therefore, thebrightness need not be corrected that much, and it is possible toprevent the image quality from being deteriorated as much as possible.

B. Modification

The above-described embodiment may have modifications as describedbelow.

(1) In the above-described embodiments, three consecutive strobeshootings are performed when the mode is set to the strobe consecutiveshooting mode. The number of consecutive shootings is not limited tothree, and any number is accepted. Further, a user may set an arbitrarynumber of strobe consecutive shootings by the key operation.

In this case, the limit value is provided corresponding to the number ofpictures to be consecutively shot, and judgment on whether or not strobeconsecutive shooting is possible based on whether or not the calculatedstrobe flash time is larger than the limit value.

(2) In addition, in the embodiment as described above, the mode is setto the pixel addition drive mode when the mode is set to the strobeconsecutive shooting mode. Alternatively, the mode may be set to thepixel addition drive mode, only in the case where it is judged thatstrobe consecutive shooting is not possible with the calculated amountof flashing.

In the case where the strobe consecutive shooting is not possible withthe calculated amount of flashing, the amount of flashing of the strobeis limited and thus adequate amount of exposure cannot be acquired.Accordingly, luminosity of the whole image data can be enhanced by pixeladdition drive, whereby a bright image can be achieved. On the otherhand, in the case where the strobe consecutive shooting is possible withthe calculated amount of flashing, strobe consecutive shooting ispossible by an ordinary drive which is not the pixel addition drive,whereby a bright image can be acquired.

In this case, in the metering operation using preliminary flashing inStep S8 in FIG. 2, image data in the CCD 5 is read out by an ordinarydrive rather than pixel addition drive.

Hereafter, the flowchart in FIG. 7 will be described. The description ofthe operations which is overlapped with the description referring to theabove-described FIG. 2 and FIG. 3 will be omitted.

When the CPU 10 judges in Step S6 in FIG. 2 that the shutter button hasbeen depressed, it performs the metering operation using preliminaryflashing (Step SA1). Note that in the modification, the mode has notbeen set to the pixel addition drive mode at this time.

Subsequently, the CPU 10 calculates the amount of flashing of strobelight to be flashed on the basis of the result of the metering operation(Step SA2). That is, the CPU 10 calculates the amount of flashing oflight to achieve appropriate exposure to the image data which has beenread out in an ordinary read out-mode in which pixels are not added.

Subsequently, the CPU 10 judges whether or not strobe consecutiveshooting is possible with the calculated amount of flashing (Step SA3).That is, it judges whether or not the voltage corresponding to theamount for flashing strobe light three times consecutively with thecalculated amount of flashing is accumulated in the built-in capacitorC.

For example, the CPU 10 judges whether or not the first strobe flashtime calculated in Step SA2 is equal to or smaller than a limit value(which is assumed to be 24 μsec herein). If the CPU 10 judges that thelimit value is equal to or smaller than 24 μsec, the CPU 10 judges thatthe voltage corresponding to the amount for flashing strobe light threetimes consecutively with the calculated amount of flashing isaccumulated in the built-in capacitor C. The CPU 10 proceeds to Step S12in FIG. 2 as described above, remaining in the ordinary read-out mode inwhich pixels are not added.

On the other hand, at Step SA3, if the CPU 10 judges that strobeconsecutive shooting is not possible with the calculated amount offlashing, that is, if it judges that the first flash time is not 24 μ orless, the CPU 10 sets the mode to the pixel addition drive mode (StepSA4).

Next, the CPU 10 again performs the metering operation using preliminaryflashing in the state of the pixel addition drive mode (Step SA5).

Subsequently, the CPU 10 calculates the amount of flashing of strobelight to be flashed on the basis of the result of the metering operation(Step SA6). That is, it calculates the amount of flashing to achieveappropriate exposure to the image data which has been read out from thepixel addition drive mode.

Subsequently, the CPU 10 judges that whether or not strobe consecutiveshooting is possible with the calculated amount of flashing (Step SA7).That is, it judges whether or not the voltage corresponding to theamount for flashing strobe light three times consecutively with thecalculated amount of flashing is accumulated in the built-in capacitorC.

For example, the CPU 10 judges whether or not the first strobe flashtime calculated in Step SA6 is equal to or smaller than a limit value(which is assumed to be 24 μsec herein). If the CPU 10 judges that theflash time is 24 μsec or less, the CPU 10 judges that the voltagecorresponding to the amount for flashing strobe light three timesconsecutively with the calculated amount of flashing is accumulated inthe built-in capacitor C, and proceeds to Step S12 in FIG. 2 asdescribed above, while remaining in the pixel addition drive mode.

On the other hand, also in Step SA6, if the CPU 10 judges that strobeconsecutive shooting is not possible with the calculated amount offlashing, that is, if the CPU 10 judges that the first flash time is not24 μsec or less, the CPU 10 limits the amount of flashing of strobelight for the first picture to 24 μsec, and proceeds to the Step SA11 inFIG. 2 as described above, while remaining in the pixel addition drivemode.

The modification enables preventing the pixel addition drive mode frombeing set unnecessarily.

(3) Furthermore, in the embodiment as described above, there is provideda correction coefficient which makes the amounts of exposure (theamounts of flashing) for the first to third pictures uniform.Alternatively, a correction coefficient table which brackets the amountsof exposure may be provided, and strobe shooting may be performed bybracketing the amount of exposure for the first to third pictures byusing the correction coefficient.

FIG. 5B shows the state of the correction coefficient table enablingbracketing the exposure. It is apparent from the correction coefficientin FIG. 5B that the correction coefficient decreases gradually.Accordingly, when the correction coefficient table is used for thestrobe shooting, it is possible to perform bracketing shooting in whichthe amount of exposure gradually decreases.

In this case, a limit value corresponding to the bracketing amount isprovided, and judgment on whether or not strobe bracketing shooting ispossible is made based on whether or not the calculated strobe flashtime is larger than the limit value.

(4) Furthermore, in the embodiment as described above, only onecorrection coefficient table is provided. Alternatively, a plurality ofcorrection efficient tables that have different correction coefficientsdepending on the flash time for the first picture may be provided.

(5) Furthermore, in the embodiment as described above, the flash timesfor the second and third pictures are corrected by multiplying thecorrection coefficient on the basis of the flash time for the firstpicture. Alternatively, the value of the correction coefficient may befinely adjusted corresponding to the voltage of the built-in capacitor Cimmediately after the strobe shooting for the first and second pictures.

(6) Furthermore, in the embodiment as described above, it is judgedwhether or not individual image data acquired by shooting has adequatebrightness, and then brightness correction using gamma correction isperformed for the image data which is judged not to have adequatebrightness. Alternatively, brightness correction using gamma correctionmay be performed to the three image data acquired by strobe consecutiveshooting, only in the case where it is judged in Step S10 that strobeconsecutive shooting is not possible with the calculated amount offlashing.

(7) Furthermore, the embodiment may be modified to combination of any ofthe modifications (1) to (6) as described above.

(8) Still further, the digital camera 1 in the above-describedembodiment is not limited to the embodiment as described above. It maybe a cell phone with camera, a PDA with camera, a PC with camera, an ICrecorder with camera or a digital video camera, or any apparatus capableof strobe consecutive shooting.

While the present invention has been described with reference to thepreferred embodiments, it is intended that the invention be not limitedby any of the details of the description therein but includes all theembodiments which fall within the scope of the appended claims.

1. An imaging apparatus comprising: an image pickup element forconverting light of an object to image data; a strobe for generating aflashing light emission by an electric charge supplied from a built-incapacitor; a shooting section for performing a strobe shooting using theimage pickup element and the strobe; a shooting control section forcontrolling the shooting section to perform consecutive strobe shootingsfor only a certain number of times; a memory section which storescorrection information for compensating for a decline in a lightemission amount of the strobe due to a voltage drop in the built-incapacitor following each consecutive flashing light emission generatedby the strobe, wherein the correction information corresponds to anumber of the flashing light emissions generated by the strobe; ajudgment section for, when consecutive strobe shootings are executed foronly the certain number of times by the shooting control section,judging whether the strobe can generate consecutive flashing lightemissions for only the certain number of times with a light emissionamount that can acquire an appropriate exposure; a first calculationsection for, when the judgment section judges that the strobe cannotgenerate consecutive flashing light emissions for only the certainnumber of times with the light emission amount needed to acquire theappropriate exposure, calculating a light emission length of time foreach flashing light emission of the strobe such that the strobe cangenerate consecutive flashing light emissions for only the certainnumber of times, by compensating a specified light emission length oftime using the correction information stored in the memory section; anda light emission control section for, when consecutive strobe shootingsare executed for only the certain number of times by the shootingcontrol section, controlling the strobe to generate each of theconsecutive flashing light emissions for only the corresponding lightemission length of time calculated for that flashing light emission bythe first calculation section.
 2. The imaging apparatus according toclaim 1, wherein the shooting section charges the built-in capacitor,whereby after charging the built-in capacitor, recharging of thebuilt-in capacitor is stopped at least until a series of consecutivestrobe shootings end.
 3. The imaging apparatus according to claim 1,further comprising: a brightness correction section which appliesbrightness correction processing using gamma correction processing toindividual image data acquired by the consecutive strobe shootings foronly the certain number of times, when the light emission controlsection controls the strobe to generate flashing light emissions foronly the light emission lengths of time calculated by the firstcalculation section.
 4. The imaging apparatus according to claim 1,further comprising: a second calculation section for calculating a lightemission length of time of the strobe corresponding to the lightemission amount needed to acquire the appropriate exposure; wherein thespecified light emission length of time is a maximum light emissionlength of time that can be set for a first flashing light emission suchthat sufficient voltage remains in the built-in capacitor for the strobeto generate a last flashing light emission, when consecutive strobeshootings are executed for only the certain number of times by theshooting control section; and wherein the judgment section judgeswhether the strobe can achieve consecutive flashing light emissions foronly the certain number of times with the light emission amount that canacquire the appropriate exposure based on a judgment of whether thelight emission length of time calculated by the second calculationsection is equal to or less than the specified light emission length oftime.
 5. The imaging apparatus according to claim 4, wherein theshooting control section comprises a preliminary flashing section whichperforms preliminary flashing of the strobe with a certain amount offlashing, and controls the shooting section to execute preliminarystrobe shooting for acquiring image data by the image pickup element,and wherein the second calculation section calculates the light emissionlength of time of the strobe corresponding to the light emission amountneeded to acquire the appropriate exposure based on the image dataacquired by the preliminary strobe shooting.
 6. The imaging apparatusaccording to claim 4, wherein the shooting control section controls theshooting section to execute the consecutive strobe shootings for onlythe certain number of times based on the light emission length of timecalculated by the second calculation section, when the judgment sectionjudges that the strobe can generate consecutive flashing light emissionsfor only the certain number of times with the light emission amountneeded to acquire the appropriate exposure.